Efficient reclamation of pre-allocated direct memory access (dma) memory

ABSTRACT

For efficient reclamation of pre-allocated direct memory access (DMA) memory in a computing environment, hot-add random access memory (RAM) is emulated for a general purpose use by reclamation of pre-allocated DMA memory reserved at boot time by notifying a non-kernel use device user that the non-kernel use device has a smaller window, stopping and remapping to the smaller window, and notifying a kernel that new memory has been added, wherein the new memory is a region left after the remap. The hot-add RAM is split into at least two continuous parts.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation of U.S. patent application Ser. No.14/252,146, filed on Apr. 14, 2014.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates in general to computers, and moreparticularly to efficient reclamation of pre-allocated direct memoryaccess (DMA) memory in a computing environment.

Description of the Related Art

In today's society, computer systems are commonplace. Computer systemsmay be found in the workplace, at home, or at school. A data processingsystem typically includes a processor subsystem having at least onecentral processing unit (CPU), an input/output (I/O) subsystem, a memorysubsystem and a bus subsystem. These data processing systems may includedata storage systems, or disk storage systems, to process and storedata. Many of these computer systems include virtual storage componentsand computing clusters. Computing clusters and virtual storagecomponents are found in a variety of computing environments.

Large amounts of data have to be processed daily and the current trendsuggests that these amounts will continue being ever-increasing in theforeseeable future. For the most part, computing systems face asignificant challenge to meet the increasingly stringent reliabilitydemands and while providing complex and sophisticated data storagesystems. In many modern computing data storage/processing, systems,certain hardware data subsystems within the computer r allowed to accessand use memory independently of the central processing unit (CPU), whichis referred to as direct memory access (DMA). Accordingly, it would bedesirable to improve computing efficiency within the data storagesystems to add physical memory, in a DMA hardware infrastructure, thatmay be required for high availability servers without compromisingreliability and data availability.

SUMMARY OF THE DESCRIBED EMBODIMENTS

In one embodiment, a method is provided for efficient reclamation ofpre-allocated direct memory access (DMA) memory, in a computingenvironment. In one embodiment, by way of example only, the methodcomprises emulating a hot-add random access memory (RAM) for a generalpurpose use by reclamation of pre-allocated DMA memory reserved at boottime by notifying a non-kernel use device user that the non-kernel usedevice has a smaller window, stopping and remapping to the smallerwindow, and notifying a kernel that new memory has been added, whereinthe new memory is a region left after the remap; and splitting thehot-add RAM into at least two continuous parts.

In addition to the foregoing exemplary method embodiment, otherexemplary system and computer product embodiments are provided andsupply related advantages. The foregoing summary has been provided tointroduce a selection of concepts in a simplified form that are furtherdescribed below in the Detailed Description. This Summary is notintended to identify key features or essential features of the claimedsubject matter, nor is it intended to be used as an aid in determiningthe scope of the claimed subject matter. The claimed subject matter isnot limited to implementations that solve any or all disadvantages notedin the background.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the invention will be readilyunderstood, a more particular description of the invention brieflydescribed above will be rendered by reference to specific embodimentsthat are illustrated in the appended drawings. Understanding that thesedrawings depict embodiments of the invention and are not therefore to beconsidered to be limiting of its scope, the invention will be describedand explained with additional specificity and detail through the use ofthe accompanying drawings, in which:

FIG. 1 is a block diagram illustrating a computing system environmenthaving an example storage device in which aspects of the presentinvention may be realized;

FIG. 2 is a block diagram illustrating a hardware structure of datastorage system in a computer system in which aspects of the presentinvention may be realized;

FIG. 3 is a flowchart illustrating an exemplary method for efficientreclamation of pre-allocated direct memory access (DMA) memory usinghot-add random access memory (RAM) in which aspects of the presentinvention may be realized;

FIG. 4 is a block diagram illustrating a hardware structure of aphysical memory with regions in which aspects of the present inventionmay be realized;

FIG. 5 is a block diagram illustrating a hardware structure of memorymap with boot-time reserved region in which aspects of the presentinvention may be realized;

FIG. 6 is a block diagram illustrating a hardware structure of a memorymap after a device driver is loaded in which aspects of the presentinvention may be realized;

FIG. 7 is a block diagram illustrating a hardware structure of a memorymap after part of the preallocated memory was reclaimed in which aspectsof the present invention may be realized.

DETAILED DESCRIPTION OF THE DRAWINGS

In a multiprocessor design, a direct memory access (DMA) mechanism isused to move information from one type of memory to another. The DMAmechanism such as a DMA engine or DMA controller also moves informationfrom a system memory to a local store of a processor. More specifically,the DMA controller may be used to transfer blocks of data between aninput/output (I/O) device and consecutive locations in the systemmemory. The direction of data transfer can be from the device to memory,or vice versa.

Without DMA, when the CPU is using programmed input/output, it istypically fully occupied for the entire duration of the read or thewrite operation, and is thus unavailable to perform other work. WithDMA, the CPU initiates the transfer, does other operations while thetransfer is in progress, and receives an interrupt from the DMAcontroller when the operation is done. This feature is useful any timethe CPU cannot keep up with the rate of data transfer, or where the CPUneeds to perform useful work while waiting for a relatively slow I/Odata transfer. Hardware systems may use DMA, including disk drivecontrollers, graphics cards, network cards and sound cards. DMA is alsoused for intra-chip data transfer in multi-core processors. Computersthat have DMA channels can transfer data to and from devices with muchless CPU overhead than computers without DMA channels. Similarly, aprocessing element inside a multi-core processor can transfer data toand from its local memory without occupying its processor time, allowingcomputation and data transfer to proceed in parallel. DMA can also beused for “memory to memory” copying or moving of data within memory. DMAcan offload expensive memory operations, such as large copies orscatter-gather operations, from the CPU to a dedicated DMA engine.

The physical devices in certain computing architectures (e.g.,PC-compatible computers) require DMA-able memory during forhigh-performance operation. The DMA-able memory means that the physicalRAM is continuous in its physical addresses. Usually such buffers areallocated within the kernel using special functions that return an arrayof physically continuous pages. The problem is that for largerequirements DMA-able memory allocation may fail due to RAMfragmentation. To solve this problem a large number of smaller buffersmay be allocated. This approach better withstands the fragmentation, butmay suffer from a deficiency in performance due to increased interruptrequest (IRQ) rate; also it may not be supported by peripheral hardwarethat requires a specific buffer size. Another solution may be for theDMA engine to use virtual and not physical addresses for a DMAoperation. One of the main drawbacks is a requirement for specialhardware on the motherboard and/or CPU. Also, not all the peripheralssupport this mode of DMA operation. An additional solution may beallocating the memory using “alloc_bootmem*” routines, which run justafter the kernel starts initializing. In other words, the alloc_bootmemcommand is a specialized command to allocate memory at boot up. Thisapproach requires the driver to be compiled into the kernel, which isnot always feasible, and does not guarantee the success of theallocation, though highly increases it. In one embodiment, a solutionmay be for using the command-line parameters to the kernel, specify arange of memory as input-output memory region. The kernel will not usethis region of the memory, as it assumes this is not a regular randomaccess memory (RAM), but memory-backed peripheral; and the driver mayremap the memory for the use of DMA. The main benefit of this approachis assured success of a large DMA-able memory allocation, and in realityis the only guaranteed way to provide a large DMA-able allocation. Yet,one major drawback is an inability to reuse this memory for the otheruses (e.g., memory that may be used for general purpose uses other thanmemory reserved for large requirements of DMA-able memory allocationthat may fail due to RAM fragmentation). As such, a need exists forreusing memory (e.g., RAM) that was reserved at boot time and now thisreserved memory at boot time may be reused for the other uses (e.g.,memory that may be used for general purpose uses).

With the enterprise-level servers getting more and more sophisticated,the need for extended serviceability becomes a must requirement. Serversthat perform online real-time processing of data may usually not affordswapping, and all the memory usage should be pre-designed andscrupulously calculated. If, however, there is a run-time need toincrease the amount of available RAM, parts of I/O buffers may bereused, trading the performance of the specific I/O device off. Thisflexibility is required for high-availability servers, and constitutes avery important tool for support personnel.

In addition, a memory controller integrated circuit (IC) may enable toexecute a hot-add memory operation, which is the adding of physicalmemory module to a running computer system. The hot-add memory may beused specifically in a Linux kernel, which us currently implemented andused for 1) supporting real RAM memory being inserted while the systemis up (online), 2) supporting an online increase of the available RAM invirtual machines (e.g., the host machine allocates a block of memory forthe specific virtual machine, and signals this event to the guest OS,and 3) accepting the signal by a special driver in the guest operatingsystem (OS), and commences the RAM discovery mechanism. Moreover, thepresent invention provides for a new use of hot-add RAM. Emulatinghot-add RAM is exercised to reclaim the pre-allocated DMA-able memoryfor generic use for guaranteeing the allocation of the DMA-able memoryof any size, while keeping the flexibility of the preallocated memoryreuse for general purpose, particularly for the sake of serviceabilityof high-availability servers. The solution enables for reducing theserver downtime comparing to an existing solution, which requireschanging the preallocation scheme and rebooting the OS kernel. As usedherein, the generic use means any allocation for the use by kernel, thedrivers, or user-space application. An example of special purpose useis, for example, memory-mapped I/O, reserved DMA-able memory. Commonfeature of “special use” in this context is not taking part of thespecial use memory in allocations for the kernel, drivers, anduser-space applications.

In other words, emulating hot-add RAM may be described as follows. Whena buffer is reserved in the way as described above, the kernel does notsee the addresses pertaining to this buffer as memory. For example, ifthere are reserved 4 GB in the computing system with 24 GB of RAM, thekernel only knows 20 GB while the other 4 GB are not a memory fromkernel's point of view. The kernel is unable to access this memory,unable to map the memory to virtual addresses, and the like. Now assumeit is decided to pass 1 GB out of the 4 GB to the kernel. It is done byemulating the hot-add memory: a continuous buffer 1 GB is freed by thedriver, and then signaling the kernel that a new (physical) RAM wasadded starting with the start of 1 GB buffer and with the length of 1GB. The latter operation emulates the addition of real physical memoryto the system, as the kernel may not distinguish between this case, andthe case when a real RAM chip is added to the system. The kernel wouldreact to this signal by sensing the memory and adding it to the poolwhere the 20 GB already reside (resulting now in 21 GB of usablememory).

In one embodiment, efficient reclamation of pre-allocated direct memoryaccess (DMA) memory using hot-add random access memory (RAM), in acomputing environment, is a achieved by using hot-add RAM for a generalpurpose use by reclamation of pre-allocated DMA memory reserved at boottime for responding to an emergency by notifying a user of a non-kerneluse device (e.g., a memory-mapped I/O device or “dev”) that thenon-kernel use device has a smaller window, stopping and remapping tothe smaller window, and notifying a kernel that new memory has beenadded, wherein the new memory is a region left after the remappingoperation.

Turning now to FIG. 1, exemplary architecture 10 of a computing systemenvironment is depicted. The computer system 10 includes centralprocessing unit (CPU) 12, which is connected to communication port 18and memory device 16. The communication port 18 is in communication witha communication network 20. The communication network 20 and storagenetwork may be configured to be in communication with server (hosts) 24and storage systems, which may include storage devices 14. The storagesystems may include hard disk drive (HDD) devices, solid-state devices(SSD) etc., which may be configured in a redundant array of independentdisks (RAID). The operations as described below may be executed onstorage device(s) 14, located in system 10 or elsewhere and may havemultiple memory devices 16 working independently and/or in conjunctionwith other CPU devices 12. Memory device 16 may include such memory aselectrically erasable programmable read only memory (EEPROM) or a hostof related devices. Memory device 16 and storage devices 14 areconnected to CPU 12 via a signal-bearing medium. In addition, CPU 12 isconnected through communication port 18 to a communication network 20,having an attached plurality of additional computer host systems 24. Inaddition, memory device 16 and the CPU 12 may be embedded and includedin each component of the computing system 10. Each storage system mayalso include separate and/or distinct memory devices 16 and CPU 12 thatwork in conjunction or as a separate memory device 16 and/or CPU 12.

FIG. 2 is an exemplary block diagram 200 showing a hardware structure ofa data storage system in a computer system according to the presentinvention. Host computers 210, 220, 225, are shown, each acting as acentral processing unit for performing data processing as part of a datastorage system 200. The cluster hosts/nodes (physical or virtualdevices), 210, 220, and 225 may be one or more new physical devices orlogical devices to accomplish the purposes of the present invention inthe data storage system 200. In one embodiment, by way of example only,a data storage system 200 may be implemented as IBM® System Storage™DS8000™ and/or the IBM® TS3500™ Tape Library. A Network connection 260may be a fibre channel fabric, a fibre channel point to point link, afibre channel over ethernet fabric or point to point link, a FICON orESCON I/O interface, any other I/O interface type, a wireless network, awired network, a LAN, a WAN, heterogeneous, homogeneous, public (i.e.the Internet), private, or any combination thereof. The hosts, 210, 220,and 225 may be local or distributed among one or more locations and maybe equipped with any type of fabric (or fabric channel) (not shown inFIG. 2) or network adapter 260 to the storage controller 240, such asFibre channel, FICON, ESCON, Ethernet, fiber optic, wireless, or coaxialadapters. Data storage system 200 is accordingly equipped with asuitable fabric (not shown in FIG. 2) or network adaptor 260 tocommunicate. Data storage system 200 is depicted in FIG. 2 comprisingstorage controllers 240 and cluster hosts 210, 220, and 225. The clusterhosts 210, 220, and 225 may include cluster nodes.

To facilitate a clearer understanding of the methods described herein,storage controller 240 is shown in FIG. 2 as a single processing unit,including a microprocessor 242, system memory 243 and nonvolatilestorage (“NVS”) 216. It is noted that in some embodiments, storagecontroller 240 is comprised of multiple processing units, each withtheir own processor complex and system memory, and interconnected by adedicated network within data storage system 200. Storage 230 (labeledas 230 a, 230 b, and 230 n in FIG. 3) may be comprised of one or morestorage devices, such as storage arrays, which are connected to storagecontroller 240 (by a storage network) with one or more cluster hosts210, 220, and 225 connected to each storage controller 240.

In some embodiments, the devices included in storage 230 may beconnected in a loop architecture. Storage controller 240 manages storage230 and facilitates the processing of write and read requests intendedfor storage 230. The system memory 243 of storage controller 240 storesprogram instructions and data, which the processor 242 may access forexecuting functions and method steps of the present invention forexecuting and managing storage 230 as described herein. In oneembodiment, system memory 243 includes, is in association with, or is incommunication with the operation software 250 for performing methods andoperations described herein. As shown in FIG. 2, system memory 243 mayalso include or be in communication with a cache 245 for storage 230,also referred to herein as a “cache memory”, for buffering “write data”and “read data”, which respectively refer to write/read requests andtheir associated data. In one embodiment, cache 245 is allocated in adevice external to system memory 243, yet remains accessible bymicroprocessor 242 and may serve to provide additional security againstdata loss, in addition to carrying out the operations as described inherein.

In some embodiments, cache 245 is implemented with a volatile memory andnon-volatile memory and coupled to microprocessor 242 via a local bus(not shown in FIG. 2) for enhanced performance of data storage system200. The NVS 216 included in data storage controller is accessible bymicroprocessor 242 and serves to provide additional support foroperations and execution of the present invention as described in otherfigures. The NVS 216, may also referred to as a “persistent” cache, or“cache memory” and is implemented with nonvolatile memory that may ormay not utilize external power to retain data stored therein. The NVSmay be stored in and with the cache 245 for any purposes suited toaccomplish the objectives of the present invention. In some embodiments,a backup power source (not shown in FIG. 2), such as a battery, suppliesNVS 216 with sufficient power to retain the data stored therein in caseof power loss to data storage system 200. In certain embodiments, thecapacity of NVS 216 is less than or equal to the total capacity of cache245.

Storage 230 may be physically comprised of one or more storage devices,such as storage arrays. A storage array is a logical grouping ofindividual storage devices, such as a hard disk. In certain embodiments,storage 230 is comprised of a JBOD (Just a Bunch of Disks) array or aRAID (Redundant Array of Independent Disks) array. A collection ofphysical storage arrays may be further combined to form a rank, whichdissociates the physical storage from the logical configuration. Thestorage space in a rank may be allocated into logical volumes, whichdefine the storage location specified in a write/read request.

In one embodiment, by way of example only, the storage system as shownin FIG. 2 may include a logical volume, or simply “volume,” may havedifferent kinds of allocations. Storage 230 a, 230 b and 230 n are shownas ranks in data storage system 200, and are referred to herein as rank230 a, 230 b and 230 n. Ranks may be local to data storage system 200,or may be located at a physically remote location. In other words, alocal storage controller may connect with a remote storage controllerand manage storage at the remote location. Rank 230 a is shownconfigured with two entire volumes, 234 and 236, as well as one partialvolume 232 a. Rank 230 b is shown with another partial volume 232 b.Thus volume 232 is allocated across ranks 230 a and 230 b. Rank 230 n isshown as being fully allocated to volume 238—that is, rank 230 n refersto the entire physical storage for volume 238. From the above examples,it will be appreciated that a rank may be configured to include one ormore partial and/or entire volumes. Volumes and ranks may further bedivided into so-called “tracks,” which represent a fixed block ofstorage. A track is therefore associated with a given volume and may begiven a given rank.

The storage controller 240 may include, be associated with, and/or incommunication with a hot-add memory (e.g., RAM memory) module 255 (e.g.,a hot-add memory RAM memory emulation module 255), a reclamation module257, a mapping/unmapping module 259, and a signaling module 261 (itshould be noted that the hot-add RAM is only emulated, therefore thestorage controller may or may not include hot-add RAM). The hot-addmemory module 255, the reclamation module 257, the mapping/unmappingmodule 259, and the signaling module 261 may work in conjunction witheach and every component of the storage controller 240, the hosts 210,220, 225, and storage devices 230. The hot-add memory module 255, thereclamation module 257, the mapping/unmapping module 259, and thesignaling module 261 may be structurally one complete module or may beassociated and/or included with other individual modules. The hot-addmemory module 255, the reclamation module 257, the mapping/unmappingmodule 259, and the signaling module 261, may also be located in thecache 245 or other components.

The storage controller 240 includes a control switch 241 for controllingthe fiber channel protocol to the host computers 210, 220, 225, amicroprocessor 242 for controlling all the storage controller 240, anonvolatile control memory 243 for storing a microprogram (operationsoftware) 250 for controlling the operation of storage controller 240,data for control, cache 245 for temporarily storing (buffering) data,and buffers 244 for assisting the cache 245 to read and write data, acontrol switch 241 for controlling a protocol to control data transferto or from the storage devices 230, the hot-add memory module 255, thereclamation module 257, the mapping/unmapping module 259, and thesignaling module 261, in which information may be set. Multiple buffers244 may be implemented with the present invention to assist with theoperations as described herein. In one embodiment, the clusterhosts/nodes, 210, 220, 225 and the storage controller 240 are connectedthrough a network adaptor (this could be a fibre channel) 260 as aninterface i.e., via at least one switch called “fabric.”

In one embodiment, the host computers or one or more physical or virtualdevices, 210, 220, 225 and the storage controller 240 are connectedthrough a network (this could be a fibre channel) 260 as an interfacei.e., via at least one switch called “fabric.” In one embodiment, theoperation of the system shown in FIG. 2 will be described. Themicroprocessor 242 may control the memory 243 to store commandinformation from the host device (physical or virtual) 210 andinformation for identifying the host device (physical or virtual) 210.The control switch 241, the buffers 244, the cache 245, the operatingsoftware 250, the microprocessor 242, memory 243, NVS 216, the hot-addmemory module 255, the reclamation module 257, the mapping/unmappingmodule 259, and the signaling module 261 are in communication with eachother and may be separate or one individual component(s). Also, several,if not all of the components, such as the operation software 250 may beincluded with the memory 243. Each of the components within the devicesshown may be linked together and may be in communication with each otherfor purposes suited to the present invention.

As mentioned above, the hot-add Memory module 255, the reclamationmodule 257, the mapping/unmapping module 259, and the signaling module261, may also be located in the cache 245 or other components. As such,one or more of the hot-add Memory module 255, the reclamation module257, the mapping/unmapping module 259, and the signaling module 261,maybe used as needed, based upon the storage architecture and users'preferences.

FIG. 3 is a flowchart illustrating an exemplary method 300 for efficientreclamation of pre-allocated direct memory access (DMA) memory usinghot-add random access memory (RAM) in which aspects of the presentinvention may be realized. The method 300 begins (step 302) by emulatinga hot-add RAM for a general purpose use by reclamation of pre- allocatedDMA memory reserved at boot time for responding to an emergency bynotifying a non-kernel use device user that the non-kernel use devicehas a smaller window, stopping and remapping to the smaller window, andnotifying a kernel that new memory has been added, wherein the newmemory is a region left after the remap (step 304). The method 300 ends(step 306).

FIG. 4 is a block diagram illustrating a hardware structure of aphysical memory with regions in which aspects of the present inventionmay be realized. FIG. 4 illustrates the memory map before reclamation ofpre-allocated direct memory access (DMA) memory using hot-add memoryfeature. The physical memory with regions show physical RAM pages 402with general use pages (e.g., general purpose use) pages 406, I/O bufferpages 408, and unused pages 410. A corresponding virtual address mappingstructure 404 is illustrated showing the virtual address mappings of thecorresponding general use pages 406, I/O buffer pages 408, and unusedpages 410 as mapped to the virtual addresses 404. The total size ofmemory is T GiB (e.g., gigabyte that is 2³⁰ bytes) 452 starting from thebase offset of 0 GiB 450.

FIG. 5 is a block diagram illustrating a hardware structure of memorymap with boot-time reserved region in which aspects of the presentinvention may be realized. Using the hardware structure of a physicalmemory with regions from FIG. 4, the physical memory 504 with regionsshow physical RAM pages 502 with general use pages (e.g., generalpurpose use) pages 506, preallocated RAM 512, and unused pages 510. Acorresponding virtual address mapping structure 504 is illustratedshowing the virtual address mappings of the corresponding general usepages 506, preallocated RAM 512, and unused pages 510 as mapped to thevirtual addresses 504. The total size of memory is T GiB (e.g.,gigabyte) 552 starting from the base offset of 0 GiB 550. A command lineparameter designated as “memmap=S$X” is used and the kernel is directedto assume “S” GiB, where S is a variable, starting at offset “X” (X+S isthe address; the size is indeed S and the offset of the initial byte inthe region X) as memory-mapped I/O device, which is designated forillustration purposes as “dev”). At this point, FIG. 5 illustrates thismemory layout showing the memory map with a boot-time reserved region(shown as the space of X GiB 554 plus X+S GiB 556). The kernel sees onlythe used pages for general use 506 and the unused pages for general use510 of physical memory 504.

The kernel boots, utilizing all the memory except the boot-time reservedregion (S GiB 556 starting at offset X GiB 554). After that, a driverfor the I/O device that requires the DMA loads (usually as a kernelmodule), and remaps the reserved RAM region (S GiB 556 starting atoffset X GiB 554) for the use of DMA, and into the virtual address space506. Then the driver configures the I/O device's DMA to use buffers fromthe reserved region (S GiB 556 starting at offset X GiB 554).

FIG. 6 is a block diagram illustrating a hardware structure of a memorymap after a device driver is loaded in which aspects of the presentinvention may be realized. FIG. 6 illustrates the state of the server atthe normal operation. The physical memory with regions shows physicalRAM pages 602 with general use pages (e.g., general purpose use) pages606, preallocated RAM 612, and unused pages 610. A corresponding virtualaddress mapping structure 604 is illustrated showing the virtual addressmappings of the corresponding general use pages 606, I/O buffer pages608, and unused pages 610 as mapped to the virtual addresses 604. Thetotal size of memory is T GiB (e.g., gigabyte) 652 starting from thebase offset of 0 GiB 650.

The memory-mapped I/O device's (e.g., non-kernel use device or “dev”)DMA uses S GiB 656 (starting at offset X GiB 654) of RAM, and the kernelutilizes T-S GiB (e.g., T GiB 652 minus S GiB 656) or all the otherpurposes (e.g., General Purpose Memory “GPM” which is general purposememory, contrary to IO buffers). S GiB 656 starting at offset X GiB 654,and this is the reserved region.

In other words, after a device driver is loaded, the preallocated pagesof the physical RAM pages are now mapped to the virtual addresses withinthe processors memory space. The I/O buffer pages 608 in the virtualmemory address, which is the same continuous memory in the physical RAM,may be accessed (e.g., read or write) by a software application, andhardware devices may access the physical memory. The hardware devicesmay access the physical pages; due to existing physical to virtualaddresses mapping, the latter is reflected in virtual space. Forexample, if a physical page with address 0x1000 (mapped to virtualaddress 0x5000) is written by hardware device, the software may read thechange at virtual address 0x5000. The hardware device is unaware ofvirtual addresses.

FIG. 7 is a block diagram illustrating a hardware structure 700 of amemory map after part of the preallocated memory was reclaimed in whichaspects of the present invention may be realized. The physical memorywith regions shows physical RAM pages 702 with general use pages (e.g.,general purpose use) pages 706, preallocated RAM 712, and unused pages710. A corresponding virtual address mapping structure 704 isillustrated showing the virtual address mappings of the correspondinggeneral use pages 706, I/O buffer pages 708, and unused pages 710 asmapped to the virtual addresses 704. The total size of memory is T GiB(e.g., gigabyte) 752 starting from the base offset of 0 GiB 750. Inother words, FIG. 7 illustrates that preallocated memory (e.g., theemergency page 760) is now released for general use 706 (e.g., theGeneral Purpose Memory) and is mapped to the virtual addresses 704 thatmay be for general use 706, and this released region 760 is unrelated tothe I/O buffer pages 708 and is no longer mapped to the I/O buffer 708(compare FIG. 7 to FIGS. 5 and 6).

In case of an emergency, which requires urgent addition of GPM onaccount of I/O buffers, the following sequence is performed. Assuming arequirement to add “F” GiB (shown in FIG. 7 as 760) of GPM, such that Fis less than S (e.g., F<S), S is illustrated as “S GiB” or X+S GiB 756,which starts at offset X GiB 754). First, the application or servicethat requires operation of the non-kernel use device is stopped. Second,a device driver stops the operation of the hardware device that uses aDMA-able memory. The driver unmaps a buffer from the kernel virtualmemory system. The driver unmaps a buffer from the kernel virtual memorysystem. The driver splits S GiB of the buffer into two continuous parts:S′ and F; and S GiB equal S′ plus F (represented in equation for asS=S′+F and F is region 760. The driver remaps S′GiB for the use of dev'sDMA (e.g., the non-kernel use device's DMA). The driver signals thekernel that a new memory was hot-added to the system, pointing to F. Thekernel scans the new memory region F GiB 760, perceives the new memoryas newly added RAM, and adds the new memory to the GPM pool, or all theother purposes (e.g., General Purpose Memory “GPM”). At this stage thedev's buffer is of size S−F, and the size of GPM is T GiB minus the SGig plus the F GiB (in equation form the GPM=T−S+F (e.g., T GiB 752 plusthe new F GiB 760 of memory). The driver reconfigures the dev with thenew DMA buffer S′. The application or service requiring the operation ofdev is restarted.

In one embodiment, for efficient reclamation of pre-allocated directmemory access (DMA) memory using hot-add random access memory (RAM)hot-add memory (e.g., RAM) for a general purpose use by reclamation ofpre-allocated DMA memory reserved at boot time for responding to anemergency by notifying a memory-mapped I/O device (e.g., non-kernel usedevice or “dev”) that the non-kernel use device has a smaller window,stopping and remapping to the smaller window, and notifying a kernelthat new memory has been added, wherein the new memory is a region leftafter the remap.

In one embodiment, in case of the emergency, performing at least one of:stopping the application requiring the non-kernel use device, stoppingoperations of the non-kernel use device by a device driver, and/orunmapping a buffer from a kernel virtual mapping system.

In one embodiment, the hot-add RAM is split into at least two continuousparts. The hot-add RAM is a physical memory that is being inserted tothe physical system when the latter is running (thus “HOT-add”).

In one embodiment, at least one of the two continuous parts of thehot-add RAM is remapped for use by DMA memory of the non-kernel usedevice, wherein the new memory is at least one of the two continuousparts.

In one embodiment, the kernel is signaled (e.g., a notification is sent)of the addition of the hot-add RAM.

In one embodiment, the present invention performs at least one of:scanning the at least one of the two continuous parts of the hot-add RAMby the kernel, perceiving that the least one of the two continuous partsof the hot-add RAM is newly added, and/or adding the least one of thetwo continuous parts of the hot-add RAM to a pool of general purposememory. In one embodiment, the present invention performs at least oneof: configuring the non-kernel use device with the buffer of the leastone of the two continuous parts of the hot-add RAM, and restarting theapplication-requiring a memory-mapped I/O device.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

What is claimed is:
 1. A method for efficient reclamation ofpre-allocated direct memory access (DMA) memory using a processor devicein a computing environment, the method comprising: emulating a hot-addRAM for a general purpose use by reclamation of pre-allocated DMA memoryreserved at boot time by notifying a non-kernel use device user that thenon-kernel use device has a smaller window, stopping and remapping tothe smaller window, and notifying a kernel that new memory has beenadded, wherein the new memory is a region left after the remap; andsplitting the hot-add RAM into at least two continuous parts.
 2. Themethod of claim 1, further including, in case of the emergency,performing at least one of: stopping the application requiring thenon-kernel use device, stopping operations of the non-kernel use deviceby a device driver, and unmapping a buffer from a kernel virtual mappingsystem.
 3. The method of claim 1, further including remapping at leastone of the two continuous parts of the hot-add RAM for use by DMA memoryof the non-kernel use device, wherein the new memory is at least one ofthe two continuous parts.
 4. The method of claim 3, further includingsignaling the kernel of the addition of the hot-add RAM.
 5. The methodof claim 4, further including performing at least one of: scanning theat least one of the two continuous parts of the hot-add RAM by thekernel, perceiving that the least one of the two continuous parts of thehot-add RAM is newly added, and adding the least one of the twocontinuous parts of the hot-add RAM to a pool of general purpose memory.6. The method of claim 5, further including configuring the non-kerneluse device with the buffer of the least one of the two continuous partsof the hot-add RAM.
 7. A system for efficient reclamation ofpre-allocated direct memory access (DMA) memory in a computingenvironment, the system comprising: at least one processor deviceoperable in the computing environment, wherein the at least oneprocessor device: emulating a hot-add random access memory (RAM) for ageneral purpose use by reclamation of pre-allocated DMA memory reservedat boot time by notifying a non-kernel use device user that thenon-kernel use device has a smaller window, stopping and remapping tothe smaller window, and notifying a kernel that new memory has beenadded, wherein the new memory is a region left after the remap; andsplits the hot-add RAM into at least two continuous parts.
 8. The systemof claim 7, wherein the at least one processor device performs at leastone of: stopping the application requiring the non-kernel use device,stopping operations of the non-kernel use device by a device driver, andunmapping a buffer from a kernel virtual mapping system.
 9. The systemof claim 7, wherein the at least one processor device remaps at leastone of the two continuous parts of the hot-add RAM for use by DMA memoryof the non-kernel use device, wherein the new memory is at least one ofthe two continuous parts.
 10. The system of claim 9, wherein the atleast one processor device signals the kernel of the addition of thehot-add RAM.
 11. The system of claim 10, wherein the at least oneprocessor device performs at least one of: scanning the at least one ofthe two continuous parts of the hot-add RAM by the kernel, perceivingthat the least one of the two continuous parts of the hot-add RAM isnewly added, and adding the least one of the two continuous parts of thehot-add RAM to a pool of general purpose memory.
 12. The system of claim11, wherein the at least one processor device configuring the non-kerneluse device with the buffer of the least one of the two continuous partsof the hot-add RAM.
 13. A computer program product for efficientreclamation of pre-allocated direct memory access (DMA) memory using aprocessor device, the computer program product comprising anon-transitory computer-readable storage medium having computer-readableprogram code portions stored therein, the computer-readable program codeportions comprising: an executable portion that emulates a hot-addrandom access memory (RAM) for a general purpose use by reclamation ofpre-allocated DMA memory reserved at boot time by notifying a non-kerneluse device user that the non-kernel use device has a smaller window,stopping and remapping to the smaller window, and notifying a kernelthat new memory has been added, wherein the new memory is a region leftafter the remap; and an executable portion that splits the hot-add RAMinto at least two continuous parts.
 14. The computer program product ofclaim 13, further including an executable portion that performs at leastone of: stopping the application requiring the non-kernel use device,stopping operations of the non-kernel use device by a device driver, andunmapping a buffer from a kernel virtual mapping system.
 15. Thecomputer program product of claim 13, further including an executableportion that remaps at least one of the two continuous parts of thehot-add RAM for use by DMA memory of the non-kernel use device, whereinthe new memory is at least one of the two continuous parts.
 16. Thecomputer program product of claim 15, further including an executableportion that signals the kernel of the addition of the hot-add RAM. 17.The computer program product of claim 16, further including anexecutable portion that performs at least one of: scanning the at leastone of the two continuous parts of the hot-add RAM by the kernel,perceiving that the least one of the two continuous parts of the hot-addRAM is newly added, and adding the least one of the two continuous partsof the hot-add RAM to a pool of general purpose memory.
 18. The computerprogram product of claim 17, further including an executable portionthat configures the non-kernel use device with the buffer of the leastone of the two continuous parts of the hot-add RAM.